The present application is directed to stress sensors and, more particularly, to apparatus, systems and methods for measuring stress.
Stress sensors may be used to measure an amount of force, torque or pressure applied to a material. Traditional stress sensors have employed a conductive wire coil that is wrapped around a separate core member. The core member is formed from a magnetostrictive material. An electrical current flowing through the wire coil establishes a magnetic field that surrounds the wire coil and propagates into the core member. A stress applied to the core member changes the magnetic permeability of the core member. The inductance of the wire coil is a function of the permeability of the material through which the coil member's magnetic field flows. Therefore, the stress applied to the core member changes the inductance of the wire coil and the change in inductance may be correlated into a measured force value.
U.S. Ser. No. 11/244,792, filed on Oct. 6, 2005, the entire contents of which are incorporated herein by reference, discloses a stress sensor in which the wire coil and core member have been functionally combined as a coilless sensor. The coilless sensor includes an electrically conductive member comprising a magnetostrictive material that is configured to receive an applied force, wherein the electrically conductive member has a change in impedance in response to the applied force. The coilless sensor further includes first and second covering members such that the electrically conductive member may be disposed between the first and second covering members. The second covering member has first and second apertures extending therethrough. The coilless sensor further includes first and second electrical terminals disposed through the first and second apertures, respectively, of the second covering member that are coupled to the electrically conductive member. The coilless sensor has increased sensitivity for measuring forces and provides more consistent force measurements since manufacturing tolerances associated with the air gap between various elements of the core member have been eliminated.
However, there remains a need for a coilless stress sensor and associated system having improved functionality and design flexibility. There is also a need for a coilless stress sensor capable of being used in an electric motor-operated brake caliper assembly.